ML20136H396
| ML20136H396 | |
| Person / Time | |
|---|---|
| Site: | Byron, Braidwood  |
| Issue date: | 03/13/1997 |
| From: | Hosmer J COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9703190132 | |
| Download: ML20136H396 (9) | |
Text
_
Commonwealth Edison Company 1400 Opus Place Dow ncrs Grove, IL 6051M701 March 13,1997 U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Attention:
Document Control Desk
Subject:
Response to Request for Additional Information Related to the Proposed Extension of the Byron 1 and Braidwood 13.0 Volt IPC License Amendment for ODSCC Byron Nuclear Power Station Unit 1 NRC Docket Number: 50-454 Braidwood Nuclear Power Station Unit 1 NRC Docket Number: 50-456
References:
1.
D. Lynch letter to I. Johnson dated February 27,1997, transmitting Request for Additional Information Pertaining to Request for Technical Specification Amendment for 3 Volt IPC Renewal 2.
D. Lynch letter to 1. Johnson dated January 27,1997, transmitting Request for Additional Information Pertaining to Request for Technical Specification Amendment for 3 Volt IPC Renewal
(
In the Reference letters the Nuclear Regulatory Commission (NRC) transmitted Requests for Additional Information (RAI) related to the proposed extension of the 3.0 volt repair limit for an additional operating cycle for Byron Unit I and Braidwood Unit 1. Attached is the Commonwealth Edison Company's Response to RAls 1 and 2 (dated February 27,1997) and RAI 12 (dated January 27,1997). If you have any questions concerning this correspondence please contact this office.
Sincer, f druf#v John B. Hosmer
/
Engineering Vice President
/
l Attachment 0
cc:
D. Lynch, Senior Project Manager-NRn i
G. Dick, Byron /Braidwood Project Manager-NRR C. Phillips, Senior Resident inspector-Braidwood S. Burgess, Senior Resident inspector-Byron A. B Beach, Regional Administrator-Rill J 90 % <J ffi e f Nuclear Safety-IDNS 9703190132 970313
}]$((ll$}l{ll${$llll PDR ADOCK 05000454 P
PDR A Unicom Company
I
\\
Attachment Response to RAI dated January 27,1997
RAI 12
l t
During the SG blowdown following a postulated main steam line break (MSLB), the pressure drop across a TSP will be determined by the position dependent flow distribution across a TSP.
Because of the differences in resistance between fluid flows parallel and perpendicular to the SG tube bundle above the topmost TSP, a multidimensional flow pattern exists. This effect will be most pronounced at the upper TSP. Accordingly, assess the effect of the multidimensional flow pattern on the position dependent pressure drop across the TSPs.
Response
l The original analysis, which was used to detemiine tube support plate loads using RELAP5M3, j
assumed the area around the U-Bend tubes above the top tube support plate (TSP) to be one volume. The maximum pressure differential across the top TSP was calculated to be 2.44 psi and uniformly applied. The loss coefficient across the U-Bend region (due to crossflow resistance) was added to the loss coefficient at the separator inlet. If a varying loss coefficient due to the U-Bend region is considered, a multidimensional flow pattern is developed during MSLB. This multidimensional flow pattern will cause a non-uniform pressure distribution across the TSP.
l l
Comed has developed a method to evaluate the effects of this multidimensional pressure l
distribution. The method involves developing a 2-Dimensional pressure distribution across the TSP l
as a function of TSP radius. This was accomplished by developing four 1-dimensional flow l
streams modeled from the N support plate to the separator, see Figure 1. Prior to the MSLB, the l
fluid in the tube bundle area adjacent to the TSP is single phase. After the MSLB begins, the liquid i
is subjected to decompression and acceleration forces. The flow rate and pressure drop across the TSP can be determined by drawing a control volume around the fluid regions and solving the l
Bernoulli integral equation which accounts for inertial and viscous effects. The volume around the TSP was divided into four control volume flow streams. These parallel flow streams were located at widening radii from the center of the bundle. Each of these control volume streams represent a vertical flow path from the N support plate to the separator. The only differences in these parallel flow streams are the bundle loss coefficients. The control volume flow stream at the center of the TSP had the largest total loss coefficient due to the proximity of the U-Bend region, while the control volume stream at the outside of the tube bundle had the smallest loss coefficient. By calculating the pressure differential across the TSP for each of these flow streams a 2-Dimensional representation of concentric regions emanating from the center was developed for the following radii: 13, 26, 39,52, and 61.375 inches, see Table 1. Based on this table it can be seen that the originally assumed TSP pressure differential of 2.44 psi actually decreases to 2.1 psi at the center of the bundle and increases to 2.64 at the outer edge of the bundle. This represents a 0.53 psi change from the center of the bundle to the outside edge of the bundle due to multidimensional influences of the tube bundle.
i K:nla\\bybwd\\stgen\\3vrrai2
l j
The method described above for determining multidimensional pressure is judged to be conservative based on the following-No cross flow was assumed between the parallel flow streams. This has the effect of j
maximizing the pressure differences between the flow steams. Cross flow between the flow streams would cause a more uniform pressure distribution across the TSP.
No pressure drops or fluid inertial terms other than the separator entrance and the N and P l
=
l TSPs were included. In reality, other significant pressure losses and inertia exist and sene to limit the transient velocity across the TSP more than taken credit for above.
l i
l Using the new loads listed in Table 1, an analysis was performed by Westinghouse to determine their effect on TSP Displacement during MSLB. Table 2 lists the maximum displacement values for each TSP along with the original analysis displacements which assumed uniform loading. Table 2 indicates that there is a slight increase, of.0048 inches, at the top "P" TSP, this represents a j
maximum of a 5% increase in displacement. The design criteria of maintaining TSP displacement below 0.100 inch is maintained for all plates with the exception of Plate A, where the maximum displacement is 0.1208" Plate A is the flow distribution baffle, the 0.100" TSP displacement i
limitation and the 3 Volt IPC interm are not applied to this location.
Conclusion When the effect of multidimensional flow is considered on TSP displacement, using conservative assumptions, the total change in TSP displacement is less than 5% and remains within the original 0.100 inch design criteria.
Response to RAI dated February 27,1997
RAI 1
In your response dated February 5,1997, to Question 7 of our request for additional information (RAI) issued on January 27,1997, Comed stated that if an axial indication was found in a steam l
generator (SG) tube at the top of the tube sheet or at an expansion joint at the tube support plates l
(TSPs), in one of the 21 expanded SG tubes in each of the four SGs at Byron 1 and Braidwood 1, the scope of the eddy current inspection (ECl) would not be expanded. These 21 expanded tubes act as additional tie rods supporting the TSPs under SG blowdcun loads which would occur following a postulated main steamline break (MSLB) and are an important element in the staff s decision to issue on November 9,1995, the Byron 1 and Braidwood I license amendments incorporating the lower voltage repair limit of 3.0 volts into the Byron 1 and Braidwood 1 Technical Specifications (TSs). Specifically, the staffs review of the license amendments cited above, focused on the importance of the structural integrity of these additional 21 tie rods.
Comed's position on this particular issue is that the presence of axial indications found in an ECI would not result in a TSP displacement exceeding 0.10 inches. This is the value which was assumed in your evaluation of the SG tube burst probability under postulated accident conditions as well as your evaluation of potential SG tube leakage.
l K:nla\\bybwd\\stgen\\3vrrai2 i
i
While this statement regarding TSP displacement may be true in itself, your response to Question 7 cited above does not address the need to expand the scope of the ECl as a result ofidentifying a potentially active stress corrosion process. The staff concern in this matter is that if an active stress corrosion process is occurring in one of the 21 expanded SC mbes acting as a tie rod, there is an increased potential for a circumferential indication to be dcveloping in one of the expanded tie rods not chosen for inspection Accordingly, discuss your plans for expanding the scope of your ECl in light of this particular staff concem.
Response
The integrity of the expanded tubes is an important element of the design basis of the 3.0 volt IPC.
Based on this, Comed will increase the eddy current inspection of the expanded tubes from twenty.
percent to one hundred percent, if either circumferential or axial indications are found in the critical areas of a Locked Tube. These critical areas are (sce Figure 2):
Area 1: the roll transition region at the top of the tube shect; Area 2: the bulges, in the parent tube and sleeve, above and below the Tube Support Plates (TSP). If either the parent tube or sleeve has an axial or circumferential indication, the inspection scope will be expanded to 100%;
and e
Area 3: the sleeve within the confines of the TSP.
Comed will notify and discuss their findings with the Staff prior to conducting an expanded j
inspection. This inspection program assures that active degradation is addressed and that the 3 Volt IPC design basis is maintained.
RAI2 1
In your response to Question 9 of our RAI dated January 27,1997, Comed indicated the conditions which would cause it to calculate the conditional failure probability of axial burst.
Specifically, Comed stated that either about 250 axial indications in the 10 to 15 volt range or one axial indication greater than 15 volts, would need to be identified before calculating this particular conditional failure probability. However, your projections for the forthcoming end-of-cycle (EOC) distribution of voltages include adjustments for: (a) the probability of detection (POD) in an ECI:
(b) flaw growth estimates determined from previous ECis; and (c) non-destructive examination (NDE) uncertainty associated with an ECl. The staff believes that the net effect of these three adjustments is to provide a conservative estimate of the EOC voltage distributions.
j Accordingly, it is not clear to the staff that your proposed subject inspection criteria are conservative. More importantly, if the licensee were to find on the order of one to five axial indications in the range of 10 to 15 volts during a forthcoming ECI, the staff would have serious concems about the applicability of the methodology used to estimate the EOC voltage distribution l
given that a very limited number ofindications is expected to be found in this voltage range if this i
methodology is sufficiently conservative. Accordingly, discuss your proposed subject inspection criteria in 1:ght of this particular staff concem.
I i
l K:nla\\bybwd\\stgen\\3vrrai2
Response
The intent of Comed's response to RAI question 9 dated February 5,1997 was to demonstrate that the axial tensile failure of a large number ofindications greater than ten volts would have a negligible comribution on the total probability of burst. The calculation was not intended tojustify having a larger number ofindications than predicted in the greater than ten volt range.
Braidwood 1 is approaching the end of cycle (EOC) 6. The EOC 6 voltage projections for the upcoming refueling outage for Braidwood Unit 1 predict that the voltage of the largest whole tube will be 8.4 volts. No indications are predicted to be greater than ten volts at the EOC 6 (refer to Braidwood letter BW/96-0033 to the Document Control Desk dated March 5,1996, transmitting Braidwood Station Unit 1 Steam Generator Interim Plugging Criteria 90 Day Report). Although the largest whole tube is predicted to be at 8.4 volts, because of the nature of the distribution, Comed does not believe that the detection of one tube at a voltage of greater than 8.4 volts is unusual.
Byron 1 is approaching the EOC 8. The EOC voltage projections for the upcoming refueling l
. outage for Byron Unit 1 predict that the maximum voltage to be seen will be 11.5 volts.. The l
number ofindications predicted greater than ten volts at the end of Cycle 8 is 6.47 (refer to Byron letter 96-5146 to Document Control Desk dated September 9,1996, transmitting the Byron Station Unit 1 Steam generator Interim Plugging Criteria 90 Day Report).
Comed will compare the predicted and actual EOC voltage distributions for Braidwood Unit 1 l
during the Spring 1997 outage and for Byron Unit 1 if the steam generators are not replaced at l
EOC 8. If the field measurements (i.e., number ofindication, size oflargest indications, distribution ofindications, etc.) are less than or equal to those predicted then no evaluation will need to be performed. If the field measurements are greater than that predicted, Comed will notify and discuss the results with the Staff, then a root cause detennination will be performed and Comed will calculate the conditional failure probability of axial burst.
l I
I h
l K:nla\\bybwd\\stgen\\3rrrai2
l Tchl31 Pressure Distribution As A Function of Radius For Plate P Radius -inch Normalind "ree.w l
0.000 0.870 13.000 0.923 26.000 0.977 l
39.000 1.030 f
52.000 1.083 i
61.375 1.083 P e A +Br, A = 0.87, B = 0.0041/ inch i
?
1.10 1.05 1
l f 1,o0 j
~
~ 0,gg
,= =
=$
f 0.90 l
I 0.85 O.0 10.0 10.0 80.0 40.0 50.0 80.0 70.0 Distance ihnn Plate Center-inch l
l
~
l
i Table 2 l
Summary of Marimum Displacements ModelD4 Steam Generator l
RELAP Loads i
LoadFactor = LA i
i i
4 Reference Analysis Versus Radial Pressurw Distribution for Plate P P
{
Radial Prsesure Plate Reference Analysis Distribution l
A 0.1208 0.1208 C
0.0568 0.0671 F
0.0680 0.0686 s
J 0.0746 0.0748 L*
0.0773 0.0777 4
i M
0.0848 0.0e50 l
N 0.0848 0.0866 i
P
.0.0884 0.0932 l
i 1
i f
)
i f
{
4 E
J i
1 i
1 9
, FIGURE 1 CONTROL VOLUME DIAGRAM Separatorinlet A=22.01 K=13.7 A=56.45 N
ControlVolume/ Path DP applied P TSP A=17 K=1.08 A=56.45
~'
N TSP A=17 K=1.08
---,y
- rw--
+w w
e - -
4 4
l l
Figure 2 l
Critical Areas of a Locked Tube l
I k
l l
i 4
l Area 2
\\\\
c 2
N, i.
1 l
I 1,
I I
,